Process for producing a screen printing form and screen printing fabric of a coated screen web

ABSTRACT

In a process for the production of a screen printing form comprising a grid-like screen web with a coating of an emulsion, in particular a photosensitive emulsion, a screen web is partially provided with at least one coating area which is composed of a plurality of separately applied coating regions. Preferably the emulsion is applied in a plurality of mutually parallel adjacent coating strips of defined width by at least one nozzle.

BACKGROUND OF THE INVENTION

The invention concerns a process for the production of a screen printingform comprising a screen web, for example of plastic filaments, bycoating with an emulsion which in particular is photosensitive. Theinvention also concerns a screen printing form comprising a coatedscreen web.

Centuries after it was first used in China the screen printing processhas been known in Europe approximately since the 19th Century, afine-mesh textile cloth or wire mesh material is stretched out in ascreen printing frame and covered in the image-free regions by astencil, so as to be impermeable to ink. Besides manual cut stencils—forexample for labelling or writing—nowadays preferably photographicallyproduced direct or indirect stencils are the usual practice; the choiceof the kind of stencil adopted—in the case of direct stencils those withemulsion, with direct film and emulsion or with direct film and water—isleft to the discretion of the screen printer.

A plurality of steps are usually required to produce a screen printingform. Firstly a screen printing cloth is stretched out over a clampingframe of light metal or alloy, wood or the like, and is glued to theframe in its stretched position. The cloth is then coated withphotosensitive emulsion, for example using a coating channel manually orby machine using an automatic coating apparatus. As the coating thereoncannot be produced exactly as far as the inward side of the frame, theremaining surface area must be subsequently sealed off using screenfiller. The coated surface is now exposed by means of a copy original(film) corresponding to the print image. The regions of the print imagewhich are not exposed are washed out. The operation of drying thestencil is followed by the retouching operation and the operation ofcovering over the edges with screen filler.

It has been found inter alia difficult to produce an exact flat layersurface on the screen cloths which are usually produced employing aso-called taffeta weave. Due to the low proportion of solids—usuallybelow 50%—in the emulsion the layer sinks down into the mesh openings ofthe cloth in the subsequent drying procedure, whereby the surface mayexhibit a certain degree of roughness. For certain areas of use, thatsurface quality may be sufficient, but for higher levels of qualityrequirement, at least one further coating operation is required.

If a plurality of small frames are to be covered with the cloth—forexample for producing print images of small surface area—, the procedureinvolves the use of a so-called mother frame, and the screen cloth isstretched out thereon; it is held to the mother frame for example byclamping clips which are described in the present applicants' EP 0 650832 A1. The smaller screen printing frames are put on to a support andthe screen web which is held under tension is fitted thereover.

A process for the production of photochemically coated material forscreen printing cylinders is disclosed in German laid-open applicationDE 3441593A. In that procedure a chromium steel wire mesh of suitablemesh size is coated with nickel electrolytically, chemically or byvapour deposition, to such an extent that the points of intersection ofthe cloth are fixed in such a way that no movement is possible; thestabilized material is then coated with at least one layer comprising aphotosensitive emulsion by applying that emulsion to a flat surface andembedding the cloth into the rear side of the layer of emulsion andjoining same by applying a further layer of emulsion, so that the resultis a flat copying layer on the surface of the screen printing stencil,which is at the printing side.

U.S. Pat. No. 3,834,348A describes a clamping frame—which is variable inwidth—with a cloth portion fixed therein using clamping elements.Displaceable over the cloth portion is a channel for a viscous fluid oran emulsion, the latter flowing out of adjacent slots in the wall of thechannel on to the cloth portion in order to form a coating thereon. Thecoating is then dried or hardened on the cloth portion.

JP 5 216 239A discloses a container with a clamping frame in which acloth is coated with a photosensitive film. The fluid is introduced intothe container until a desired layer thickness has been produced on thecloth. The fluid is then partially exposed; the unexposed regions areremoved after termination of the treatment so as to result in an image.

SUMMARY OF THE INVENTION

The foregoing object is attained by the teaching of the independentclaims; the appendant claims set forth advantageous configurations.

In accordance with the invention a screen web is partially providedwithin a predetermined outline contour with coating areas comprising theemulsion, wherein the emulsion is applied preferably in web form or alsoin point form to the screen web. It is advantageous to use at least onenozzle for the application procedure, which nozzle is guided parallel tothe longitudinal direction of the screen web over the screen cloth andproduces laterally mutually adjoining coating strips which together givethe coating area.

The coating areas can be produced in different ways. On the one hand—inthe case of low levels of requirement, rough surface—they can be applieddirectly to the screen web and then dried. It is also possible for thosecoating areas which are applied directly to the screen web to be linedwith a protective foil and only then moved to the drying station; thatis done in particular when the situation involves high levels ofrequirement and a good roughness value on the Z-axis. It is particularlyadvantageous however for the coating areas to be produced on a strongstable carrier material and for the latter to be fed with the wetemulsion regions to the screen web; those emulsion regions are thentransferred on to the screen web and subsequently dried. Then, thecarrier material is drawn off or however provisionally kept as aprotective foil on the screen web.

It is in accordance with the invention for a center line of the coatingarea produced—defined by its preferably four contour lines—to include anangle of inclination with a longitudinal edge of the screen web; thecontour lines are turned about the center of the coating area throughthat angle, which is preferably less than 45°.

In accordance with the invention, application of the coating areas at anangle of inclination relative to the screen web permits the coated clothportions to be stretched out in an angled position on a clamping frame.Cloths which are stretched out in an angled condition permit cleaner andtidier printing of lines which have to be printed parallel to the screenprinting frame. The crucial consideration is that in that situationthere is no parallelism between the yarn path of the screen cloth andthe line to be printed.

A simplification in manufacture is achieved in particular when thecoating area is composed of individual coating webs which are eachproduced by a respective nozzle or the like tool and which are adjacentin parallel relationship and the longitudinal edges of which blend intoeach other so that no contour strips which pass through the coating arearemain.

In accordance with a further feature of the invention each narrow edgeof the strip-like coating web is associated with a respective one of thecontour lines of the coating area which is angled relative to the axisof the mother frame.

It is in accordance with the invention for the center line of a clampingframe associated with the coating area to be positioned on the centerline of the contour of the coating area, which clamping frame isarranged at a spacing relative to the contour lines and is then glued tothe screen web in the taut condition thereof outside the coating area.After the screen web regions which remain between the frame and thecoating area have been covered over by an impermeable layer, a coatedprinting stencil, in particular for smaller surface areas, is producedin a simple fashion, wherein the number of contour lines of thepolygonal coating area can be different.

In particular cases the coating areas can also be produced in anotherfashion; the screen web is provided at a surface with a continuousemulsion layer from which then the regions which do not belong to apredetermined pattern of the coating areas are removed.

It is particularly advantageous for those excessive zones of the coatingto be sucked away immediately after the application thereof, that is tosay with the emulsion in the moist condition.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, advantages and details of the invention will beapparent from the following description of preferred embodiments andwith reference to the drawing in which:

FIG. 1 is a plan view of an apparatus for stretching out a coated screenweb period portion with groups of clamping devices,

FIG. 2 is a diagrammatic side view of an installation for coating ascreen web,

FIGS. 3 and 4 show plan views of a screen web with coating areas,

FIGS. 5 and 6 show other plan views of the screen web which is shown ona reduced scale in comparison with FIGS. 3 and 4,

FIG. 7 shows a screen web on an enlarged scale in comparison with FIGS.3 to 6 with a plurality of coated regions for associated clampingframes,

FIG. 8 shows a plan view on a larger scale than FIG. 7 of a coatedregion,

FIG. 9 shows a diagrammatic view corresponding to the view shown in FIG.2 of another installation, and

FIG. 10 is a plan view of the FIG. 9 installation.

DETAILED DESCRIPTION OF THE EMBODIMENTS

An apparatus 10 for stretching out a rectangular fabric portion or ascreen web 12 of preferably gauze-like screen material for use in thescreen printing process has—along the four sides of a support frame 14—aplurality of clamping elements or clamping devices 16. They each engage,with a respective clamping jaw 18, a portion of the screen web 12 in theedge region thereof and tension the screen web 12 which is then fixedtherearound by displacement of a respective pulling cylinder 19 in thepulling direction x. The screen web 12 whose surface is provided withcoating areas 20 lies on the mother frame 14 and is drawn downwardlyfrom the outside edge thereof towards the clamping jaw 18 in the closedposition thereof at an angle (not shown) of about 6°.

Reference 22 denotes a control unit which is fed from a line 24 withcompressed air at a maximum of 10 bars and from which three controllines 25, 25 _(a), 25 _(b) for the clamping devices 16 extend.

As shown in FIG. 2, fed to the screen web 12 is a web-like carriermaterial 28 which is coated in a coating station 30 in an applicationprocedure to be described hereinafter, with regions of photosensitiveemulsion which are not shown in the drawing for the sake of claritythereof. Those regions correspond in regard to their dimensions andspacings relative to each other, for example to the coating areas 20 onthe screen web 12 in FIG. 3. The carrier material 28 which is coatedwith those regions passes on to the screen web 12 at a lining station32; under pressure, the layer of photosensitive emulsion is transferredon to the screen web 12 and then dried in a through-run station 34.

Downstream of the through-run station 34 the coating areas 20 arepresent in the configuration previously occurring on the carriermaterial 28, on the screen web 12, they can now be separated from thecarrier material 28 or discharged with same as a temporary protectivelayer.

The drawing does not show a process operating procedure for coatingareas which are applied to the screen web 12 directly—without anyfoil-like carrier material; in that case, downstream of the coatingstation 30, the screen web is immediately conveyed to the drying orthrough-run station 34 or upstream thereof it is provided with aprotective foil which can be removed after the drying procedure.

FIG. 3 diagrammatically shows a screen web 12 of the web width b withcoating areas 20 which are arranged parallel to the longitudinal axis Athereof; six of the coating areas are provided within a so-called repeator period portion 36 of the length z. One of those coating areas 20 isemphasized by grating hatching, for the sake of improved claritythereof. Disposed by way of example around the coating area 20 which isarranged to the right of the hatched area is a clamping frame 38 towhich that portion of the taut screen web 12 is then connected by anadhesive operation.

FIGS. 4 to 6 show further kinds of coating areas 20, 20 _(a). Thecoating areas 20 _(a) are composed of individual webs or strips 46 whichare described in greater detail with reference to FIGS. 7 and 8; thisinvolves coating strips 46 which in the coating operation are put on tothe open cloth 12 _(a) and which can no longer be seen after the coatingarea 20 _(a) is finished, merging into same. The photosensitive coatingis applied by means of a ‘universal’ nozzle in coating strips 46. Thecoating areas 20 are therefore tailored to size in relation to therespective use involved, as also applies in relation to FIG. 6.

FIGS. 4 to 6 also indicate smaller coating areas 20 _(a) correspondingto those in FIG. 3, in a position of being inclined relative to thelongitudinal axis A or the parallel longitudinal edges 13 of the web(FIG. 4), as well as larger coating areas 20, 20 _(a) of which thereis/are only one or two per repeat or period portion 36.

FIG. 7 shows a repeat or period portion 36 of a screen web 12 of thefree web length a of here about 1400 mm and the free web width b of 900mm with edge regions 11 of widths a₁ and b₁ respectively, associatedwith clamping elements 16. The repeat or period portion 36 is stretchedout on a support frame 14. Disposed at top left is a mother frame 40 asan edging border of an auxiliary plate 41 of wood or plastic material;the clamping frames 38—which then have the repeat or period portion 36positioned thereover—are positioned on the auxiliary plate 41 during theproduction procedure.

Shown on the free surface of the screen cloth or the screen web 12—tothe left of the longitudinal axis A₁ of the mother frame 40—are threesquare coating areas 20 which are delimited by a contour with fourcontour lines 42, consisting of photosensitive emulsion—preferably ofthe kind set forth in the opening part of this specification—as aphotosensitive coating of a width e of here 180 mm, which in the slackcondition of the screen web 12 are arranged relative to each other atcenter spacings i of 380 mm—and i₁ of 394 mm in the taut condition. Thespacing f of the center line M of those three coating areas 20, whichcenter line is parallel to the longitudinal axis A of the system,relative to the—also parallel—center line M of a second row of coatingareas 20 which can be seen to the right of the longitudinal axis A₁corresponds to the center spacings i and i₁ respectively both in thetaut and also in the slack condition. The central coating areas 20 ofboth rows of areas are disposed on the transverse axis Q of the motherframe 40, relative to which each two contour lines 42 of each of thesquare coating areas 20 are disposed in parallel relationship.

Each of the coating areas 20 is to be so arranged within the contour ofa small clamping frame 38 which lies on the auxiliary plate 41 and isdisposed beneath the screen web 12, in such a way that the clampingframe can be readily glued to a non-coated zone of the screen printingcloth, outside the coating area 20; in order to be able to apply theadhesive to the screen cloth 12 without affecting the coating area 20, acoating-free cloth edge portion 44 of a minimum width h should remainaround the coating area 20—and in the glued condition, therearound, afree edge portion of a width h₁.

In order clearly to illustrate the described joining procedure involved,FIG. 7 shows by way of example coating areas 20 of printing stencils fordirect printing on Compact Discs; diagrammatically shown on theright-hand side are the coating areas 20 within their clamping frame 38,wherein the lower frame 38 _(a) or the frame center line B is turned outof the center line M through an inclination angle w of in this case22.5° about the center point Z of the coating area 20, in such a waythat the corners 43 of the coating area 20 are at a spacing—even ifslight—relative to the insides of the frame; the inside length m of theclamping frame 38, 38 _(a) is here 260 mm, with an outside length n of310 mm.

The minimum width h of the above-mentioned cloth edge portion 44 is halfthe difference between the outside length n and the area width e. Halfthe difference thereof, relative to the inside length m, in turn givesthe free edge width h₁.

The coating areas 20 are to be so arranged with their contours withintheir clamping frame 38, 38 _(a) that they are disposed therearound at aspacing h₁, which can involve problems for example in the case ofinclined arrangements in accordance with the frame 38 _(a). For thatreason, a coating area 20 _(a) which is shown inter alia in FIG. 8, withany position of the frame center line B with an inclination angle w byway of example of 22.5° is produced by the emulsion that forms it beingapplied by an applicator member (not shown) guided parallel to the weblongitudinal axis A—to the carrier material 28 described with referenceto FIG. 2—in integral coating strips 46 of a small width t. Thedifferent lengths q of the coating strips 46 which are adjacent inparallel relationship are adapted to the respective position of theturned contour lines 42 _(a) and the narrow edges 48 of each coatingstrip 46 touch different contour lines 42 _(a). Disposed within them isa circle as the boundary 50 of the actual print image (not shown) forthe Compact Disc.

Not shown in this connection is a construction in which the emulsion isapplied approximately in punctiform manner within the contour lines 42_(a). The drawing shows a fluid-impermeable layer 56 which surrounds thecoating area 20, 20 _(a) and covers over the coating-free cloth edgeportion 44.

FIGS. 9 and 10 represent an alternative which can possibly be used, tothe above-described process. Here the carrier foil 28 is provided in thecoating station 30 over its entire surface or in the form of a widestrip with a layer 52 of a width c consisting of that emulsion, and isthen immediately passed through a suction removal station 54. In thestation 54, individual coating areas 20 _(b) are produced by suctionremoval of the layer regions which are not wanted, in regard to apreselectable pattern of the coating areas 20 _(b).

What is claimed is:
 1. A process for the production of a screen printingform comprising a screen web of plastic filaments, by coating with aphotosensitive emulsion, characterized in that the screen web ispartially provided with at least one coating area which is composed of aplurality of separately applied coating strips, wherein the emulsion isapplied as the coating strips in an adjacent, substantially parallelrelationship and are thereafter dried.
 2. A process according to claim 1characterized in that the emulsion is sprayed on approximately in pointform.
 3. A process according to claim 1 characterized in that theemulsion is applied by at least one nozzle which is guided parallel to alongitudinal edge of the screen web.
 4. A process according to claim 1 acharacterized in that the coating areas are applied to a web-likecarrier material and are transferred from same on to the screen web,whereupon the latter is dried.
 5. A process according to claim 4characterized in that the web-like carrier material is pulled off thescreen web carrying the coating areas.
 6. A process according to claim 4characterized in that the carrier material is joined as a protectivefoil to the screen web.
 7. A process according to claim 1 characterizedin that the center line of the coating area is oriented at an inclinedangle relative to the longitudinal axis of the web, which is less than30°.
 8. A process according to claim 1 characterized in that the coatingstrips include an inclined angle with the center line of the coatingarea.
 9. A process according to claim 8 characterized by an inclinedangle of less than 30°.
 10. A process according to claim 8 characterizedin that each coating strip has a narrow edge which is associated with arespective contour line of the coating area.
 11. A process according toclaim 10 characterized in that the length of each coating strip isadapted to the position of the contour line which is determined by theinclined angle.
 12. A process according to claim 10 characterized inthat the center line of a clamping frame which is associated with thecoating area and which is arranged at a spacing relative to the contourlines is put on to the center line of the contour of the coating area.13. A process according to claim 12 characterized in that the clampingframe is glued to the screen web outside the coating area.
 14. A processaccording to claim 12 characterized in that an impermeable layer whichsurrounds the coating area is applied to the screen web within theclamping frame.
 15. A screen printing product comprising a screen web ofplastic filaments, which is coated with a photosensitive emulsion, whichhas been produced according to the process of claim 1 characterized inthat the screen web is provided with coating areas composed of aplurality of coating strips.
 16. A screen printing product according toclaim 15 characterized in that the coating areas are produced on afoil-like carrier material and transferred on to the screen web, thecarrier material forming a protective foil.
 17. A screen printingproduct according to claim 15 characterized in that the coating stripsinclude an inclined angle to the center line of the coating area.
 18. Ascreen printing product according to claim 15 characterized in that thecoating strips extend at an inclined angle relative to the center lineof a clamping frame receiving them.
 19. A screen printing productaccording to claim 15 characterized in that the coating strips extendapproximately parallel to the longitudinal axis of the screen web.
 20. Ascreen printing product according to claim 15 characterized in that thescreen web is provided with a liquid-impermeable layer of a cloth edgeportion, said layer surrounding the coating area.
 21. A process for theproduction of a screen printing form comprising a screen web of plasticfilaments, by coating with a photosensitive emulsion, characterized inthat the screen web is provided with a layer of the emulsion, producinga plurality of coating areas by subsequent removal of parts of the layerof emulsion and thereafter drying the screen web.
 22. A processaccording to claim 21 characterized in that the layer of the emulsion issubdivided into the coating areas by partial suction removal.
 23. Aprocess according to claim 21 characterized in that the emulsion issprayed on approximately in point form.
 24. A process according to claim21 characterized in that the emulsion is applied by at least one nozzlewhich is guided parallel to a longitudinal edge of a carrier.
 25. Aprocess according to claim 21 characterized in that the center line ofthe coating area is oriented at an inclined angle relative to thelongitudinal axis of the web, which is less than 30°.
 26. A processaccording to claim 21 characterized in that each coating area comprisesa plurality of substantially parallel coating strips wherein the coatingstrips are at an inclined angle with the center line of the coatingarea.
 27. A process according to claim 26 characterized by an inclinedangle of less than 30°.
 28. A process according to claim 26characterized in that each coating strip has a narrow edge which isassociated with a respective contour line of the coating area.
 29. Aprocess according to claim 28 characterized in that the length of eachcoating strip is adapted to the position of the contour line which isdetermined by the inclined angle.
 30. A process according to claim 28characterized in that the center line of a clamping frame which isassociated with the coating area and which is arranged at a spacingrelative to the contour lines is put on to the center line of thecontour of the coating area.
 31. A process according to claim 30characterized in that the clamping frame is glued to the screen weboutside the coating area.
 32. A process according to claim 30characterized in that an impermeable layer which surrounds the coatingarea is applied to the screen web within the clamping frame.
 33. Aprocess for the production of a screen printing form comprising a screenweb of plastic filaments, by coating with a photosensitive emulsion,characterized in that a web-like carrier material is provided with alayer of emulsion, producing a plurality of coating areas in the carriermaterial by subsequent removal of parts of the layer, and transferringthe coating areas from the carrier material on to the screen web anddrying.
 34. A process according to claim 33 characterized in that thelayer of the emulsion is subdivided into the coating areas by partialsuction removal.
 35. A process according to claim 33 characterized inthat the emulsion is applied by at least one nozzle which is guidedparallel to a longitudinal edge of the carrier material.
 36. A processaccording to claim 33 characterized in that the center line of thecoating area is oriented at an inclined angle relative to thelongitudinal axis of the web, which is less than 30°.
 37. A processaccording to claim 33 characterized in that each coating area comprisesa plurality of substantially parallel coating strips wherein the coatingstrips are at an inclined angle with the center line of the coatingarea.
 38. A process according to claim 37 characterized by an inclinedangle of less than 30°.
 39. A process according to claim 37characterized in that each coating strip has a narrow edge which isassociated with a respective contour line of the coating area.
 40. Aprocess according to claim 39 characterized in that the length of eachcoating strip is adapted to the position of the contour line which isdetermined by the inclined angle.
 41. A process according to claim 39characterized in that the center line of a clamping frame which isassociated with the coating area and which is arranged at a spacingrelative to the contour lines is put on to the center line of thecontour of the coating area.
 42. A process according to claim 41characterized in that the clamping frame is glued to the screen weboutside the coating area.
 43. A process according to claim 41 incharacterized in that an imperable layer which surrounds the coatingarea is applied to the screen web within the clamping frame.
 44. Ascreen printing product comprising a screen web of plastic filamentswhich is coated with a photosensitive emulsion, which has been producedaccording to the process of claim 33 characterized in that the screenweb is provided with coating areas composed of a plurality of coatingstrips.
 45. A screen printing product according to claim 44characterized in that the coating strips include an inclined angle tothe center line of the coating area.
 46. A screen printing productaccording to claim 44 characterized in that the coating strips extend atan inclined angle relative to the center line of a clamping framereceiving them.
 47. A screen printing product according to claim 44characterized in that the coating strips area comprise a plurality ofsubstantially parallel coating strips which extend approximatelyparallel to the longitudinal axis of the screen web.
 48. A screenprinting product according to claim 44 characterized in that the screenweb is provided with a liquid-impermeable layer of a cloth edge portion,said layer surrounding the coating area.